Marine platform structure

ABSTRACT

A motion compensating hoist for moving a load between relatively vertically movable points, in which a cable from a tensioning hoist is interconnected between the two points, and the cable from a load hoist is connected to the load, and the tensioning hoist and the load hoist are cooperable to establish movement of the load corresponding to the relative movement between the two points and to cause further movement of the load between the two points.

1*Apr. 16, 1974 [56] References Clted UNITED STATES PATENTS 1 MARINE PLATFORM STRUCTURE Inventors: Charles D. Barron, Huntington r hf nn oea LU 1 m n, mka m tt a were A m Hm a Bo n n cclw aarl eeaa BBCC 2,854,154 9/1958 Hepinstall....,........................ 2,945,675 7/1960 Fischer.......... 1,999,936 4/1935 Primary Examiner-Frank E. Werner [73] Asslgnee: f Byron Long Beach Attorney, Agent, or Firm-Donald W. Banner ea bh C wh mw a.m m w Wm mP T m C AEO Rom Th S Bna Amt t ma eV y md ov C a n1 .wm t m w [Am 9 O0 9 1 m f WM e mmm i uh 0mm n .I. .mm m PmM ms haa TPh a C n 0 N 22 Filed: u] 8 1971 cable from a tensioning hoist is interconnected be- 1 J y tween the two points, and the cable from a load hoist is connected to the load, and the tensioning hoist and the load hoist are cooperable to establish movement 21 Appl. No.: 160,641

Related U.S. Application Data v of the load correspondmg to the relatlve movement Division of Scr. No. 19,582, March 16, 1970, Pat. No. 3,675,900.

between the two points and to cause further movement of the load between the two points.

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The present application is a divisional application of Ser. No. 19,582, and entitled Motion Compensating Hoist. Said application Ser. No. 19,582, is now US. Pat. No. 3,675,900, issued July 11, 1972.

BACKGROUND OF THE INVENTION In the transfer of a load between two relatively movable points, such asthe transfer of cargo or personnel between a well drilling platform or barge which is located in a body of water and a vessel floating in the water along 'side the platform or barge, problems are encountered caused by the rise and fall of the vessel on the surface of the water. When the water is rough, the problem' is aggravated. Essentially, the problem involves the difficulty encountered in moving the load, such as the cargo or personnel, through a comparatively short distance to and from the rising and falling deck of the vessel. In many instances, the transfer of equipment or personnel between a floating vessel and a stationary platform or larger floating vessel in the water has heretofore been practically impossible to accomplish in the presence of large waves, particularly when the waves occur at rapid intervals.

SUMMARY OF THE INVENTION 'nel between a platform or barge or large floating vessel and a smaller'floating vessel or boat.

More particularly, the invention provides a motion compensating hoist system whereby a load to be transferred between the platform and the boat is caused to move synchronously with the boat during the period that the load is being initially moved from or finally placed upon the boat. In accomplishing the foregoing, synchronous movement of the load with the boat is accomplished by a unique combination of a tensioning hoist coupled to'a load hoist.

More particularly, an elevator device adapted to be connected to the load or to contain the load is carried by the load hoist-line or cable and a tensioning hoist line or cable is connected to the boat; The tensioning hoist is driven through a clutch which is'adapted to constantly slip with a given variable torque output so as to maintain a substantially constant tension on the tensioning hoist line extending between the boat and the platform. Load sensing means are responsive to the tension on the tensioning hoist line to provide a continuous signal which is compared to a preset load value to automatically adjust the torque capacity of the clutch and thereby maintain tension on the hoist line at substantially the preset value. The load hoist is connected by drive means to the tensioning hoist and such drive means are selectively operable to establish unitized drive of the tension hoist and the load hoist. resulting in the synchronous movement of the load with the boat,

and means are provided to super-impose on the synchronous movement controlled raising or lowering of the load from or to the deck of the vessel.

Such a motion compensating hoist system enables the effective transfer'of cargo and personnel between a platform and a floating boat or vessel in a much safer manner than has been heretofore proposed. Since the load is synchronously moving with the boat, the load experiences no hard landings or impact with the boat as the load is moved to or from the boat, and the tensioning line or cable which connects the boat to the platform is available for use as a guide for the load to direct the movement of the load to or from a precise location on the boat, as well as to prevent spinning of the load.

This invention possesses many other advantages, and has other purposes which may be made more clearly apparent from a consideration of a form in which it may be embodied. This form is shown in the drawings accompanying and forming part of the present specification. It will now be described in detail, for the purpose of illustrating the general principles of the invention; but it is to be understood that such detailed description is not to be taken in a limiting sense, since the scope of the invention is best defined by the appended claims.

BRIEF DESCRIPTION OF TI-IEDRAWINGS FIG. 1 is a perspective, fragmentary view, showing a platform or barge above the water and equipped-with the invention for moving a load'to or from a boat afloat in the water;

FIG. 2 is an end elevation of the power unit and the hoist and tension winches;

FIG. 3a is a fragmentary view in side elevation, as taken on the line 3-3 of FIG. 2, on an enlarged scale, and showing the tension winch, with parts broken away;

FIG. 3b is a fragmentary view, as taken on the line 3-3 of FIG. 2, constituting a continuation of FIG. 3a, and showing the hoist winch and its drive connection to the tension winch; and

FIG. 4 is a diagrammatic illustration of the combined winches and control means therefor.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring first to FIGS. 1 and 2, there is generally illustrated a barge or platform P adapted to be supported above the water on a number of suitably located legs L which extend to the bottom of the water, and on which the platform or barge P is mounted. In the case of certain. barges, the platform is adapted to be elevated to a selected height above the water on the legs L, a dis-. tance of feet more or less. On the barge or platform may be located the usual well drilling and/or completion or workover apparatus (not shown), as is well known in the art. It will also be understood that the platform P may consist of a large vessel afloat on the water.

Periodically, the workers on the platform must be transported between the platform and the shore, and in addition. it becomes necessary from time to time to move various gear between the shore and the platform. Thus. a boat or vessel V is in part illustrated, and such boats or vessels range considerably in size from com paratively large work boats adapted to move heavy gear and supplies between the shore and the platform,

is more pronounced. The greater the frequency of the swells the worse the problem, so that under many commonly encountered conditions, the transfer of equipment or personnel between the platform and the boat or vessel V is very difficult, if not impossible to accomplish.

The present invention contemplates a motion compensating hoist system whereby an elevator E or other load support is adapted to be raised or lowered between the outer extremity of a boom 8 and the vessel V, the elevator E being suspended by a load hoist cable or line 10. A tensioning line or cable 11 extends between the outer extremity of the boom B and a point or attachment 12 to the deck of the boat or vessel V. The lines or cables and 11 respectively, are controlled by load hoist means LH and tensioning hoist means TH, whereby during the initial stages of the lifting of the elevator E from the deck of the vessel V and during the final stages of movement of the elevator E onto the deck of the vessel V, the elevator is caused to move synchronously with the vertical movement of the vessel V, i.e., the elevator E moves in the same direction and at the same rate that the vessel V moves, as the vessel V is subjected to wave action. Superimposed on the synchronous movement of the elevator E with the vessel V is independent movement of the elevator E in a controlled manner whereby the elevator E is moved smoothly and gently to or from the deck of the vessel V by the load hoist means LH. The load hoist means LH is also operable, when the elevator E is moving through the portion of its travel safely above the deck of the vessel V to independently cause vertical traverse of the elevator E.

More particularly, the boom B is mounted on suitable support structure 13 which is affixed to a side of the platform P. The boom comprises in the illustrative embodiment a pair of laterally spaced outwardly convergent V-shaped arms 14 and 15, which are preferably fabricated from upper and lower rails 16 and 17 reinforced by suitable struts 18 for rigidity, the arms 14 and being suitably connected to the support structure 13. Also supported on the support structure 13 is a power unit platform 20'on which ismounted a power source 21 such as an engineadapted through a suitable reduction gear box 22 and a chain drive 23, by way of illustration, to drive the hoist means consisting of the tensioning hoist means TH and the load hoist means LH previously referred to. At a suitable elevated and laterally displaced position relative to the support structure 13 is mounted a control cab C in which an operator has good vision of the hoisting operations. Located between the boom arms 14 and 15 and extending from the support structure 13 horizontally to a location below the outer extremity of the boom B is a walkway W. having a laterally enlarged loading deck 26 at its outer extremity. The walkway W, the power unit platform 20, as well as the barge or platform P are all provided with suitable guard rails thereabout, and a stairway 27 leads between the deck of the platform or barge P and the power unit platform 20.

The load hoist line or cable ltll extends from the load hoist means LH over an inner sheave 28 which is appropriately rotatably supported over the load hoist means LH, and extends outwardly of the boom B and over the outer sheave 29 which is rotatably supported at the outer extremity of the boom B. A hook or other load supporting means 30 is connected to the elevator E or other load so as to raise and lower the latter; The tensioning line 11 leads from the tensioning hoist means TH over a sheave 31, then along the boom B and over an outer sheave 34 which is rotatably supported at the outer extremity of the boom B. The tensioning line 11 extends downwardly from the sheave 34 and is provided with a hook 35 or other suitable means adapted to effect the connection of the tensioning line 11 to the vessel V at the location 12 previously referred The elevator E comprises a floor 36 having a cage structure 37 extending upwardly therefrom and connected to the top 38 of the elevator, the top having reinforced support members 39 connected to the hook 30 centrally of the elevator E. At one side, the elevator E has a tubular guide 40 extending vertically and through which the tensioning line 1 1 extends. Thus, the elevator is prevented from swinging or spinning on the hoist line or cable 10, and the location on the deck of the vessel V at which elevator E will land is established, notwithstanding any tendency of the vessel V to move in any direction away from a location directly beneath the outer end of the boom B.

Referring to FIGS. 3A and 38, it will be seen that the support structure for the hoist means includes three laterally spaced uprights or posts 41, 42 and 43. The up rights 41 and 42 have mounted thereon a pair of laterally spaced bearing blocks 41a and 42a in which is rotatably journalled a horizontally extended tensioning hoist shaft 44. The tensioning hoist means TH includes a drum 45 on which the tensioning line or cable 11 is wound. the hub 46 of the drum 45 being keyed as at 47 to the shaft 44 for rotation therewith. The shaft 44 extends through the bearing block 41a to provide a driven shaft end 48 adapted to be driven by the drive means 23 under the control of slip clutch means SC.

More particularly, the drive means 23 includes a drive chain 49 adapted to be driven by the output sprocket (not shown) of the reduction gear box 22 of the power source 21. This chain 49 is engaged with a sprocket 50, the hub 51 of which is rotatably mounted on the shaft end 48 by bearings 52. Affixed to the I sprocket 50, is a disc 54 whichis in turn affixed by fasteners S5 to the outer periphery of the back-up plate 56 of the slip clutch means SC.

This slip clutch means SC includes an outer annular body 57 to which an annular flange 58 is connected by fasteners 59 in opposed relation to the plate 56. lnternally thereof. the body 57 has a splined connection 60 with the outer periphery of an axially shiftable clutch pressure plate 61. Between the clutch plates 56 and 61 is a clutch friction disc 62 having friction facing 63 on opposite sides thereof and having. as at 64, a splined connection with a hub 65 which is disposed upon the shaft end 48 and is keyed thereto by a key 66. T hus. rotation from the sprocket 50 will be transmitted to the tensioning hoist shaft 44 when the slip clutch means SC is engaged to transmit rotation from the clutch body 57 and its plates 56 and 61 to the friction disc 62.

Engagement of the slip clutch means SC is accomplished by an annular expansible actuator tube 67 havthe heat of friction caused by slippage of the clutch SC. These passages 56a and 61a are defined respectively between the clutch plates and a wear disc 56b carried by the plate 56 and a wear disc 61b carried by the plate 61, the friction material on the friction disc 62 being engaged with the wear discs 56b, 611;.

Such cooled, slip clutches are well known, and generally are provided with a coolant circulating system including a stationary coolant connector member 71 through which coolant flows to and from a rotary connector member 72 which is connected, as by fasteners 72a, to the clutch flange 58 and which has conduit means 73 and supplying coolant to the passages 56a and 61a, as well as conduit means for the return flow of coolant to the stationary coolant connector 71 and thence to a heat exchanger. In addition, the rotary connector member 72 provides a connection for air conduit means -74 which leads to the air inlet 68 for the clutch actuator tube 67 from a stationary air inlet fitting 75. As is well known, the torque transmitting capacity of such slip clutches varies with the pressure of air in the actuator tube 67.

Preferably, the slip clutch means SC is made in accordance with the disclosure-of US. Pat. Application Ser. No. 19,601, filed Mar. 16, 1970, in thename ofC. D. Barron, now US. Pat. No. 3,648,814, issued Mar. I4, 1972, so that the clutch plates and discs are more effectively cooled.

Referring to P10. 38, it will be seen the motion compensating drive means MC'are adapted to selectively drivingly connect the shaft 44 of the tensioning hoist means TH to a shaft 80 of the load hoist means LH.

This shaft 80 is mounted for rotation in bearing blocks j 42b and 4312 which are mounted on the supports 42 and 43 so that the shaft 80 extends in parallel relation to the shaft 44 in laterally spaced relation. It will be understood that the relationship between the tensioning hoist means and the load hoist means is only illustrative of a preferred arrangement under given conditions, but that the shafts 44 and 80 may be co-axially or otherwise arranged. i

More particularly, the motion compensating drive means MC comprises aclutch assembly 81 including an adaptor sleeve 82 which" is keyed, as at 83, to the shaft 44 for rotation therewith. Typically, the clutch assembly 81 also includes a plurality of clutch discs 84. Alternate discs 84 are splined to the adaptor sleeve 82, and

the'other discs 84 are splined to an annular clutch body 85, whereby rotation is transmitted to the body 85 from the shaft 44 when the discs 84 are engaged between the usual back-up plate 86 and the shiftable pressure plate 87. In order to engage the clutch discs 84 between the plates86 and 87, actuator means responsive to fluid pressure are provided including a thrust bearing 88 which is engaged with the pressure plate 87 to shift the latter towards the back-up plate 86 in response to corresponding movement of an outer actuator sleeve 89' connection 92 to effect engagement of the clutch 81.

Suitably mounted on the driven clutch body 85, as by fasteners 93, is a sprocket 94. A drive chain 95 is engaged with the sprocket 94 and with'a similar sprocket 96 which is suitably affixed to the end 97 of the lift hoist shaft 80, as by a key 97a, whereby the shaft 80 will be driven by the tensioning hoist means Tl-l when the releasable connection provided by the clutch 81 is engaged. Such rotation of the shaft 80 is adapted to cause operation of the load hoist means LH synchronously with the tensioning hoist means TH during the initial stage of movement of the elevator E from the deck of the vessel V and during the final stage of movement of the elevator E towards the deck of the vessel.

In the preferred construction, the load hoist means is so arranged that the motor means for raising and lowering the load when the motion compensating drive means MC is disconnected is also operable when the motion compensating drive means is connected, whereby to superimpose on the synchronous movement of the load with the vessel V, further movement to move the load relative to the vessel. The load hoist means LH, therefore, includes a drum 100, corresponding to the drum 45 of the tensioning hoist means TH, and the load hoist line 10 is wound on this drum 100. Support flanges 101 are provided within the drum 100, these flanges being connected to or having formed at their inner periphery bearing rings 102 engageable with bearing assemblies 103, whereby the drum is rotat'ably supported on the shaft 80 so as to be rotatable relative to the shaft. At one end of the drum 100 is the usual brake drum or flange 104 with which winch drums are provided. In the presen't'case however, the flange 104 is modified internally to provide internal gear teeth 105. These teeth 105 provide for connecting both reversible hydraulic motor means 106 and normally engaged brake means 107 to the drum 100. Such motor means 106 and-brake means 107 are both car-- ried by a plate 108 which is mounted at its inner periphery-on the shaft 80, a key 109 being provided to cause rotation of the plate108 with the motor mea'ns106 and brake means 107 in the direction and at the-rate of the shaft'80, the direction and rate of rotation of which is a function of the direction and rate of rotation of the tension hoist means shaft 44.'

More particularly, the motor means 106 includes a housing 110 connected by fasteners 110a to the plate 108 and an output shaft 111 which extends through the plate 108. On the output shaft 111 is a pinion 112 which is drivingly in mesh with the internal gear teeth 105 of the drum flange 104. Fluid is supplied to the motor 106 in a selected direction through conduits 113 and 114 to effect reverse operation of the motor, such fluid being supplied through passages 113a and 114a which extend longitudinally in the shaft 80 and are supplied from stationary source conduits 113k and 114b, respectively, which are connected to a rotary fluid connector 115 suitably mounted on the housing 90b, as by fasteners 116. Such a rotary connector 115 is common and requires no further specific discussion. The motor 106 also has a fluid outlet 117 which, as will be more fully described hereinafter, supplies fluid to the inlet conduit 118 of the brake means 107 to release the latter when the motor 106 is operating, whereby the drum 100 is revolvable about the drum shaft 80 in addition to being revolvable with the shaft 80. When the motor means 106 is operating, the net rotary motion of the drum 100, is a function of the direction and extent of rotation of the shaft modified by the direction and extent of rotation of the drum 100 about the shaft in either direction. Therefore, the load hoist line 10 and the elevator may be raised or lowered by the motor 106, while the hoist line is also moving the elevator E in unison with movement of the boat or vessel V.

The brake means 107 comprises a housing 120 secured to the plate 108 so as to revolve with the shaft 80. Carried by and rotatably disposed in the housing 120 is a shaft 121. This shaft 121 extends through the plate 108 and has a pinion gear 122 keyed thereon as at 122a, the shaft being journalled in bearings 123 within the housing 120. A rotary brake member 124 is secured on the shaft 121 for rotation therewith by a key 125. Friction discs 126 are interposed between the brake rotor 124 and an actuator member 127, alternate discs being splined to the rotor 124 and to the housing 127, so that when the discs are engaged, the rotor 124 will be held stationary, thereby holding the pinion 122 against rotation, to brake the hoist drum 100. The brake 107 is normally engaged by a number of coiled compression springs 128 spaced circumferentially of the actuator member 127 and acting on the same and on an internal flange 129 in the housing 120 to bias the member 127 in a brake-engaging direction. To disengage the brake means 107, fluid under pressure is supplied from the conduit 118 to a sealed-piston chamber 130 in which is a piston 131 connected to the actuator member 127, as by screws 132, to move the actuator member 127 to a brake-release position. When the brake means 107 is engaged, the hoist drum 100 is effectively connected to the shaft 80 for rotation therewith, but when the brake means 107 is released, the motor means 106 is effective to not only connect the drum 100 to the shaft 80, but also be effect relative rotation thereof, as previously described.

The load hoist means LH also includes brake means 135 for holding the shaft 80 stationary when the motion compensating drive clutch means 81 is disengaged, during the periods that the elevator E is high enough above the boat or vessel V as to be safely raisedor lowered by the motor means 106, without compensating for relative movement of the boat beneath the boom.

Such brake means 135 includes a rotor 136 keyed, as at 137, to the outer extremity of the hoist shaft 80, and a stationary brake housing 137 connected to the support 43 by fasteners 139. Friction discs 140 are interposed between the rotor 136 and an actuator 141, alternate discs being splined to the rotor 136 and to the housing 138. A number of circumferentially spaced springs 142 are interposed between the actuator member 141 and an internal flange 143 in the housing 138 to normally bias the member 141 towards the rotor 136 to engage the brake and hold the drum shaft 80 against rotation. Fluid under pressure supplied through a conduit 144 to a sealed piston chamber 145 acts on a piston 146, which is connected to the member 141 by fasteners 147, to move the member to a brake-released position, when, as will be later described, fluid under pressure is supplied to the piston chamber 91 of the motion compensating drive clutch means 81 to engage the latter to rotate the drum shaft 80 synchronously with the tensioning hoist drum shaft 44. While the brake means 135 is shown as being spring set and pressure released, the brake means may be of the type adapted to be engaged by fluid pressure. The significant point is that the brake means 135 is released when the clutch means 81 is engaged, and vise-versa, as will be later described.

Operation The operation of the load compensating hoist system will be further understood with reference to FIG. 4, wherein the apparatus is schematically illustrated together with operating and control means therefor.

In this view, it will be noted that air under pressure is supplied to the inlet connector 74 of the slip 'clutch means SC through controller or pressure regulator R1, so that the slip clutch means may be adjusted to transmit sufficient torque to the drum shaft 44 as to maintain a predetermined tension on the tension line 11 of the tension hoist means TH which is connected to the vessel V. The controller R1 needs no specific illustration but is preferably of the type that will cause an-outlet pressure which is a function of a SET POINT" signal and a signal derived from tension on the tension line 10. The line tension on the tension hoist TH is selected so as to be proportionate to the total load represented by the elevator E, namely, the weight of the elevator E together with the weight of the load to be carried in the elevator, and inertia forces to be overcome in accelerating the load when the system is compensating for movement of the vessel V.

In order to cause motion compensating motion of the load line 10, whether or not it is connected to a load or to the elevator, the clutch means 81 of the motion compensating drive MC is engaged and the brake means 135 for the load hoist shaft is released. This is accomplished in the case of a spring loaded brake means 135 by a control valve CV1 which is interposed between a suitable source of air under pressure and the pressure conduits 92 and 141., the valve CV1 being operable in one position to connect the air supply to both the clutch means 81 to engage the same and the brake means 135 to release the same, and conversely, in the other position, to exhaust the clutch and brake to allow release and engagement thereof, respectively. Thus, with the clutch means 81 engaged, the drum shaft will rotate in the same direction and at the same rate as the tension hoist drum 45, as the latter is caused, al-

ternately. to turn in one direction by the pull on the line 11 by the vessel V. as the vessel moves downward, and in the other direction, as the vessel rises on a wave. the tension on line 11 remaining substantially constant at the value established for the slip clutch means SC.

With the load hoist line 10 thus moving with the vessel V, the line 10 may be raised or lowered, whether or not connected to the elevator E, by the operation of the reversible hydraulic motor 106, when the brake means 107 is released, whereby the load hoist drum is caused to rotate about the shaft 80, a motion which is superimposed on the shaft motion caused by the rise and fall of the vessel V.

To accomplish this, a control valve CV2 is adapted to control the flow of hydraulic motor fluid to the motor means 106 and to the brake means 107, and from the motor means to a reservoir. The valve means CV2 has a position for directing fluid from a suitable pressure source through conduits 11% and 113 and to an exhaust to cause motor rotation in one direction,

and another position for directing fluid through the conduits 11419 and 114 to cause motor rotation in the other direction. In either event, motor fluid is also supplied to the brake inlet conduit 108 from a shuttle valve SV interposed between the conduits 113 and 114.

For moving the load hoist line 10 independently of the tension line 11, the control valve CV1 is operated to relieve operating air pressure from the clutch means 81 and the brake means 135, so that the drum 100 may be driven independently of the tension hoist means, to raise or lower the'load line 10 when it is safely above the vessel V, whether the line 10 be loaded or unloaded.

With the foregoing in mind, it will now be understood that the tension on the tension line 11 caused by the application of'a controlled air'pressure to the slip clutch means SC is preferably maintained at a constant value whether or not the load hoist line 10 is supporting a load. Accordingly, load sensing means LS are provided to cause the application of a variable air pressure to the slip clutch means SC to adjust the torque capacity of the slip clutch means SC so that the pressure supply to the slip clutch mean is decreased, if the tension on line 11 tends to increase, or the pressure supply to the slip clutch means is increased, if the tension on the line tends to decrease.

Such load sensing means maybe any typical devices adapted to sense load on a line to produce a related signal, such as a load cell of the hydraulic type, as indicated at 150 in FIG. 4. This load cell 150 has a piston 151 which projects from the cylinder 152 and is engaged by a portion 31a of a lever 3112 which supports the above described tension line sheave 31'on the axle 310, the lever being pivotally mounted on a pin 31d carried by the support structure, as is obvious. Leading from the load cell cylinder 152 is a conduit 153 which is connected to a pressure regulator or transmitter R2 of any suitable type which, as is well known, is operative to regulate the drop in air pressure supplied from a source 154 and establish an outlet air signal pressure in a conduit 155 which is a function of the applied hydraulic pressure from the load sensor means LS. The air pressure from the regulator-R2 provides a signal which is conducted by the conduitl55 to the controller R1 to modify the net output pressure from the controller R1 to the slip clutch means SC.

Assuming that the vessel V, with a load thereon, such as certain equipment or personnel to be elevated to the platform P is situated at a location below the boom B, the tension line 11 is lowered. either first or with the load line 10, and the tension line 11 is connected to the vessel V. Air is supplied at a controlled value to the slip clutch means SC causing a tension on the line 11 proportionate to the weight of the elevator E and any load which it is to lift, or proportionate to the load to be lifted if the load is to be engaged by a lift device such as a hook. At this time, the rise and fall of the vessel V will cause the tension drum 45 to oscillate. The motion compensating clutch means 81' is engaged, and the drum shaft brake means 135 correspondingly released, so that the load hoist drum will oscillate in unison with the tension hoist drum 45, causing synchronous movement of the load line with the tension line, corresponding to movement of the vessel. While suchsynchronous motion occurs, the load hoist drum motor 106 may be supplied with fluid, and the brake means 107 is released, to enable controlled downward movement of the elevator E, or other load support, to the deck of the vessel for loading.

Thereafter, the motor 106 is reversed, causing upward movement of the load relative to the vessel, while the load continues to rise and fall synchronously with the rise and fall of the vessel. As the load is lifted from the deck of the vessel, the load will require an increase in the torque output of the slip clutch means SC. There is, at the same time, a resultant tendency to reduce the tension on the tension line 11, which tendency is sensed by the load sensor. means 152. The reduced hydraulic signal from the load cell 150 causes a decrease in the air pressure supplied from the transmitter R2 to controller R1 and a resultant increase in the air pressure supplied from the controller R1 to the slip clutch means until the torque capacity of the slip clutch SC is sufficient to not only maintain the initial tension on the line 11, but also to elevate the load, while the motion compensation continues. When the load is at a safe distance above the vessel, and motion compensation is no longer necessary, the brake means for the load hoist shaft are engaged and the motion compensating clutch means 81 are released. At this time, since the slip clutch means SC no longer is subjected to the load, the entire torque from the slip clutch is applied to the tension drum 45 tending to increase the tension on line 11, but the load cell will sense the increase in tension, resulting in an increased hydraulic signal to the transmitter R2 and a reduction in the net air pressure supplied to the slip clutch means from the controller R1 to the original value, whereby the tension on line 11 will be held substantially at the constant value through all modes of operation, since the clutch and the hoist means driven thereby are effectively in a closed loop,

feed back system which constantly seeks to maintain a constant tension on the tension line 10, the system adjusting for load and increased and decreased tension caused by the rise and fall of a vessel relative to a fixed platform, or differences in the rise and fall of two vessels, i.e., relative vertical movement between the two locations.

The lowering of a load onto the vessel will simply involve reversal of the operations described above in elevating a load. i

location adjacent to the loading platform 26 of the boom B and a location on the deck of the vessel V, the sliding connection between the elevator and the tension line 11 provided by the tube 40, will prevent the elevator or other load from spinning on the load line 10. In addition, the load is guided to a precise location on the deck of thevessel, notwithstanding movement of the vessel beneath the end of the boom.

For the sake of safety,it will be unders'tood that fail safe means (not shown) may be provided. In this connection, it is customary that hoist winches have normally engaged or spring-set band brakes associated with the drum, and more particularly with the flange 104 of the hoist drum 100 and with the corresponding flange 45a of tensioning hoist drum 45. Such brakes may be also employed in the present apparatus and released responsive to the fluid pressure in the operating system, so that the band brakes would automatically set in the event of loss of pressure in the system or any portion thereof. The brake'on the load hoist drum should be able to support the maximum load, but the brake on the tensioning hoist drum should be capable of slipping to allow downward movement of the vessel.

We claim:

1. In an offshore structure including a platform located above the water, a boom projecting from a side of said platform, hoist means including load hoist means having a load line depending from said boom for connection to a load, tensioning hoist means including a tension line depending from said boom and connectable to a vessel on the water beneath said boom, drive means for driving said load hoist means and said tensioning hoist means in unison to effect synchronous movement of said load and said vessel, and means operable on said hoist means to superimpose on said syn chronous movement of said load and said vessel movement of said load relative to said vessel, said drive means including slip clutch means, motion compensating drive means for releasably drivingly connecting said tensioning hoist means to said load hoist means for nected and released.

12 leased and when said motion compensating drive means connects said tensioning hoist means to said load hoist means.

2. In an offshore platform structure as defined in claim 1, said slip clutch means including a fluid pres sure actuator for varying the torque transmitting capacity of said slip clutch means in response to changes in pressure applied to said actuator, and further including means responsive to the tension on said tension line for maintaining a substantially constant tension on said line when said motion compensating drive means is con- 3. In an offshore platform structure as defined in claim 1, said load hoist line having a load support, and including means slidably connecting said load support to said tensioning hoist line.

4. In an offshore platform structure as defined in claim 1, said boom having a loading platform, said load hoist line having an elevator supported thereby, said elevator having means slidably engaged with said tensioning hoist line to prevent spinning of said elevator relative to said loading platform. 

1. In an offshore structure including a platform located above the water, a boom projecting from a side of said platform, hoist means including load hoist means having a load line depending from said boom for connection to a load, tensioning hoist means including a tension line depending from said boom and connectable to a vessel on the water beneath said boom, drive means for driving said load hoist means and said tensioning hoist means in unison to effect synchronous movement of said load and said vessel, and means operable on said hoist means to superimpose on said synchronous movement of said load and said vessel movement of said load relative to said vessel, said drive means including slip clutch means, motion compensating drive means for releasably drivingly connecting said tensioning hoist means to said load hoist means for unitized operation, and said means for effecting movement of said load relative to said vessel includes separate drive means for said load hoist means to drive the latter when said motion compensating means are released and when said motion compensating drive means connects said tensioning hoist means to said load hoist means.
 2. In an offshore platform structure as defined in claim 1, said slip clutch means including a fluid pressure actuator for varying the torque transmitting capacity of said slip clutch means in response to changes in pressure applied to said actuator, and further including means responsive to the tension on said tension line for maintaining a substantially constant tension on said line when said motion compensating drive means is connected and released.
 3. In an offshore platform structure as defined in claim 1, said load hoist line having a load support, and including means slidably connecting said load support to said tensioning hoist line.
 4. In an offshore platform structure as defined in claim 1, said boom having a loading platform, said load hoist line having an elevator supported thereby, said elevator having means slidably engaged with said tensioning hoist line to prevent spinning of said elevator relative to said loading platform. 